Rollable, single-coated hot melt adhesive film with no interlayer

ABSTRACT

The invention provides a monolayered thermoplastic hot-melt adhesive film without a separating layer which can be rolled up and unrolled without the additional use of a separating layer and in which the polymer matrix of copolyamides and/or copolyesters contains an additive combination of 0.4 wt. % to 8.0 wt. % of a spacer and 0.05 wt. % to 1.0 wt. % of a separating and lubricating agent, and optionally up to 1 wt. % of other additives, each with respect to the total mixture.

This invention provides a monolayered thermoplastic hot-melt adhesivefilm made from thermoplastic copolyamides and/or copolyesters which ismodified by the addition of additives in such a way that it can beprepared without an additional separating layer, does not block on thereel and nevertheless retains its ability to hot- bond, as a propertywhich is required for its application according to the invention, suchas two-dimensional fixing or bonding of other substrates.

Plastics films are known in many variants and for many applications. Oneparticular embodiment is hot-melt adhesives or hot-melt films, which areunderstood to be films made from thermoplastic plastics which aresuitable, in the molten state, for bonding other substrates due to thesurface tackiness and flow properties which are then present and totheir thickness. The properties and advantages of hot-melt adhesivefilms and methods for their preparation from current hot-melt adhesivegranules or powders are described, for example, in U.S. Pat. No.4,379,117 or DE 2 114 065. The use of hot-melt adhesive films isexplained by way of example in DE 3 911 613. A general categorisation ofadhesives can be found, for example, in G. Habenicht; Kleben:Grundlagen, Technologie, Anwendungen, Springer Verlag, Berlin, 1986.

The low softening or melting points of these hot-melt adhesive films orhot-melt films means that the films block on the reel. Furthermore,these materials have the disadvantage that they have very smoothsurfaces which thus contribute to the blocking characteristics of thefilms. This impairs the running properties of machines handling them.Therefore the films have to be guided permanently by moveable parts orstrips of separating material in order to prevent bonding to stationaryparts and thus interrupting the process.

The prior art for processing these blocking materials to givemonolayered strips is the use of separating layers such as, for example,are mentioned in DE 2 114 065. Separating layers consist, for example,of fabrics, films or siliconised papers.

The disadvantage of separating layers is that they themselves have to beproduced, which leads to an increase in the cost of the hot-meltadhesive films produced. In addition, they are mostly undesirablebecause the separating layers have to be rolled up separately and oftenhave to be disposed of as waste. Since these separating layers can neverbe fully recycled, they represent both a financial and ecologicalburden.

An alternative to the use of separating layers is to provide tacky orblocking materials with lubricating or antiblocking agents such as, forexample, described by Botz in Taschenbuch der Kunststoff-Additive,Gachter, Muiller (eds.), 2nd. edition, Hanser Verlag, Munich, 1983, p.229-274, of the type which are known to prevent blocking on the reel andproduce a lubricating effect on machines. The adhesive properties of thefilms are modified by the use of such materials. The disadvantage ofsystems disclosed hitherto is that they modify the adhesiveness orsealability of the material or strength of the seal produced, due tocoating the surface, in such a manner that they do not achieve theinitial level of materials which have not been treated as a result ofhaving to adjust the process parameters such as pressure, temperatureand time.

A generally widespread procedure is also the integration of tacky andblocking materials into multi-layered structures in which the variouslayers only bond in the warm and do not block against each other in thecold. Thus, U.S. Pat. No. 4 629 657, EP 0 424 761 or EP 0 263 882describe polyolefin films which are coated with hot-sealable materials.In this case, the less tacky layer takes on the function of a separatinglayer. These films have the disadvantages that they have only onehot-sealable face, also the bond adhesion which can be achieved is lowand the end product has a not inconsiderable tendency to roll.

Therefore there is the object of providing a monolayered film with highadhesive power for heat laminating, sealing and fixing which can berolled up and unrolled without adhering to itself and can be passedthrough current processing machines with a low likelihood of blocking.

According to the invention, it is possible to provide a monolayeredhot-melt adhesive film made from copolyesters and/or copolyamides whichhas no separating layer and which adequately satisfies the requirementsmentioned, which is characterised in that it can be rolled up andunrolled without adhering and without the additional use of a separatinglayer and the polymer matrix of copolyamide and/or copolyester containsan additive combination of 0.4 wt. % to 8.0 wt. % of a spacer and 0.05wt. % to 1.0 wt. % of a separating and lubricating agent, and optionallyup to 1 wt. % of other additives, each with respect to the totalmixture.

In a preferred embodiment, an additive combination is used which ischaracterised in that it contains 0.4 wt. % to 8.0 wt. % of a silica and0.05 wt. % to 1.0 wt. % of a long-chain and/or cyclic fatty acid amide.

In a particularly preferred embodiment, an additive combination is usedwhich is characterised in that it contains, in addition to the specifiedlong-chain and/or cyclic fatty acid amide, 0.02 wt. % to 0.4 wt. % of asoap as a separating and lubricating agent.

In a preferred embodiment, the additives are incorporated into thepolymer matrix of copolyesters and/or copolyamides by means of amasterbatch, characterised in that the additive batch is built up from35 wt. % to 80 wt. % of copolyester and/or copolyamide, 20 wt. % to 50wt. % of silica, 2 wt. % to 10 wt. % of a long-chain and/or cyclic fattyacid amide and 0.5 wt. % to 5 wt. % of soap.

Suitable starting materials for the polymer matrix are the correspondingthermoplastic hot-melt adhesives which are currently available on themarket from known suppliers and are available, for example, under thecommercial names Dynapol®, Vestamelt®, Platamid®, Bostik and Griltex®.The adhesive raw materials used according to the invention arepreferably thermoplastic copolyamides and/or copolyesters.

The viscosity of polymer matrix materials is generally characterised bythe melt flow index (NMFI) and the melt viscosity. The melt flow indicesof the polymer matrix components are preferably between 1.5 g/10 min and150 g/10 min, measured according to DIN 5 37 35 at 160° C. and with atest weight of 2.16 kg. The melt viscosities of the polymer matrixmaterials are preferably between 400 Pa.s and 1000 Pa.s, measuredaccording to ISO 1133 at a temperature of 160° C.

Furthermore, hot-melt adhesive raw materials which have athermoanalytically determined maximum main melting point of between 80°C. and 130° C. are preferred.

Suitable spacers are natural silicas, synthetic silicas and polymericspacers. Natural silicas are preferably used. Fats, waxes and soaps aresuitable as separating and lubricating agents. Long-chain and/or cyclicfatty acid amides which contain aliphatic groups with a carbon chainlength of preferably 14 to 20 carbon atoms are preferably used. Suitablethird additive components are soaps with a chain length of 12 to 20carbon atoms. In a preferred form, these soaps are preferably present asthe calcium salt.

Due to the use of the additive combination according to the invention,it is possible to prepare hot-melt adhesive films which not only havegood machine-running properties, but also do not require the otherwiseconventional separating layers which, as is known, increase themanufacturing costs of the films to a not inconsiderable extent. To aperson skilled in the art, who has received the relevant training andexperience, it would not be obvious that the antiblocking/separatingagent combination according to the invention would not have along-lasting negative effect on the adhesive properties of themixture/film formulations according to the invention.

Normal thermal forming processes for processing plastics are suitablefor preparing hot-melt adhesive films according to the invention. Inparticular, melt extrusion is suitable for incorporating and mixing theadditives into the polymer matrix. Incorporation of the additives maytake place as a compounding procedure using all the components or, in apreferred form, by adding a masterbatch during the manufacturingprocess.

Films according to the invention can be prepared by the flat filmprocess or the blown film process. In a preferred embodiment, the filmsare prepared by the blown film process. The blown film process enablesflexible adjustment of the width produced to the requirements of themarket due to the use of different blow-up ratios.

The breakdown of the thermoplastic hot-melt adhesives which is requiredfor the blown film process can be performed with the aid of suitablescrew moulding tools such as are described, for example, by Wortberg,Mahlke and Effen in: Kunststoffe, 84 (1994) 1131-1138. Moulding toolsfor extruding the melts into films are described, inter alia, byMichaele in : Extrusions-Werkzeuge, Hanser Verlag, Munich 1991.

In a preferred embodiment, films according to the invention have a totallayer thickness between 15 μm and 200 μm.

The surface properties of films according to the invention can beadapted to the substrates to be bonded with the aid of familiar surfacetreatment processes, preferably corona, flame and/or fluorine treatment.Various processes for surface modification are described, for example,by Gerstenberg in: Coating 4/93, p. 119-122.

The invention also provides a process for preparing composites from anysubstrates and a film according to the invention, characterised in thatthe film is assembled with at least one substrate under the effects ofheat and preferably only slight pressure. In a preferred embodiment, thefilm is laid between two different substrates and bonds these afterbeing assembled as a unit under the effects of pressure and heat.

The substrates are preferably continuous strips of material or sectionsthereof. These types of continuous strip materials are, for example,woven materials, non-wovens, films, papers, cardboards and cardboardpackaging. They also consist of cellulose or cellulose-containingproducts, other plant products, fibrous materials, plastics or evenmetals.

The invention also provides sections or cutouts of films, generallyobtained by stamping out or cutting and their use for fixing and/orsealing materials or objects to each other, characterised in thatsections or cutouts of films according to the invention are placedbetween two identical or different materials or objects and bonding inthe form of sealing or fixing takes place under the effects of heat andoptionally pressure. Suitable substances of this type for bonding arepreferably cellulose or cellulose-containing products, woods, plant andanimal fibrous materials, plastics, metals and glasses.

Composites and/or connections according to the invention arethermoreversible. They can therefore be taken apart again after use sothat the materials used are then available for materials recycling.

EXAMPLES Example A

A film was prepared by the blown film process, this being produced froma thermoplastic copolyester, which had been built up from the componentsbutanediol, terephthalic acid and isophthalic acid, with a MFI of 18g/10 min, measured according to DIN 53 735 at 160° C. with a test weightof 2.16 kg. The thermoanalytically determined melting point of thecopolyester was 125-130° C. 10 wt. % of an antiblocking batch was addedto this polymer matrix, the batch consisting of 53 wt. % of copolyesterwhich had been built up from the components butanediol, terephthalicacid and isophthalic acid, 40 wt. % of silica, 5 wt. % of long- chainfatty acid amide and 2 wt. % of calcium stearate. All the componentswere mutually plasticised in an extruder using a three-zone screw. Atubular film was formed from the melt with the aid of a blown filmmoulding tool. The ring-shaped product was cooled by blowing airthrough, then it was laid flat and cut in the edge region so that twostrips of film could be separated. These were rolled onto separatewinding devices. The film obtained had a thickness of 50 μm.

Comparison example B

The thermoplastic copolyester described in example A was plasticised,using an extruder, without the addition of further processing aids. Atubular film was produced from the melt with the aid of a blown filmmoulding tool. This tubular film could not then be laid flat since itwould not pass smoothly through the machinery due to the high degree oftackiness.

Comparison Example C

Using a two-layer blown film moulding tool, a film was prepared in whichthe first layer was formed from a thermoplastic copolyester as describedin example B. The material used was melted using an extruder.

The second layer was formed from a LD polyethylene with a density of 0.9g/cm³ and a MFI of 2 g/10 min, measured according to DIN 53 735 at 160°C. with a test weight of 2.16 kg. This material was plasticised in asecond extruder.

The two melt streams were laid one on top of the other in a two-layerblown film head and discharged from this. The ring-shaped product wascooled by blowing air through, then laid out flat and cut in the edgeregions so that two film strips could be separated. These were rolledonto separate winding devices. The thickness of each individual layerwas 50 μm. The comparison properties were tested using thecopolyester-based layer; the polyethylene based layer was peeled offbeforehand.

The following properties were tested using samples prepared from theexample and comparison examples:

Unrolling Behaviour

The unrolling behaviour was determined using a roll of film clamped inan unrolling device by manually unrolling.

Softening Range

The values cited for the softening range on a Kofler heating bank arebased on the in-house method described below. (Film) pieces of theplastics to be tested, with an area of at least 1 mm², are laid on aKofler heating bank. When these pieces have lain on the Kofler heatingbank for at least 60 s, a scalpel is used to determine at which positionon the heating bank the plastics test pieces can be plastically deformedfrom the side without exerting a large force. The position on the Koflerheating bank is then correlated with a temperature. The maximum andminimum values determined for different test pieces give the upper andlower ends of the softening range.

Peel Force

To determine the peel force, samples with a width of 4 cm and a lengthof at least 5 cm were cut out of the films in the examples. Thesesamples were laid between two textiles made from cotton in such a waythat a 5 cm long border of textile projected on one side. Then thetextiles and film were bonded together at a pressure of 220 g/cm² and atemperature of 170° C. for a duration of 20 s to 200 s, using alaboratory press. One projecting layer of textile is then clamped in aholder which is connected to a spring balance. The other projectinglayer of textile is then pulled until the bonded section of laminaterips apart. The force required for this corresponds to the peel forceand is read off from the spring balance. Depending on the duration ofthe bonding process, the highest peel force was used for comparisonpurposes.

The data characterising the properties according to the invention of thefilms which are given in the following table show clearly thatpreparation of the film according to the invention described in theexample is an advantage as compared to that of films prepared in thescope of the comparison examples and at the same time they havecomparable adhesive properties.

TABLE 1 Properties of the films prepared in the scope of the example andcomparison examples Method of Comparison Comparison Propertydetermination Units Example A example B example C Prepared ./. ./. no noyes with separating layer Can be ./. ./. yes no yes unrolled SofteningKofler bank/ ° C. 104-105 ./. 103-106 range in-house method Peel forcein-house N 49 ./. 50* method *after separation from the PE separatinglayer.

What is claimed is:
 1. A monolayered thermoplastic hot-melt adhesivefilm comprising: (a) a polymer matrix consisting essentially of at leastone of copolyamides and copolyesters; and (b) an additive combinationof, (i) 0.4 wt. % to 8.0 wt. % of a spacer, (ii) 0.05 wt. % to 1.0 wt. %of a separating and lubricating agent, and (iii) optionally up to 1 wt.% of a soap, each wt. % being with respect to the total mixture, whereinsaid adhesive film is free of a separating layer, and said adhesive filmcan be rolled up and unrolled without the additional use of saidseparating layer.
 2. The film of claim 1 wherein said spacer (b)(i) issilica, and said separating and lubricating agent (b)(ii) is along-chain and/or cyclic fatty acid amide.
 3. The film of claim 1wherein said soap (iii) is present in an amount of 0.02 to 0.4 wt.percent.
 4. A method for making the film of claim 3 comprisingintroducing an additive combination into said matrix by means of amaster batch containing: 35 to 80 percent of at least one memberselected from the group consisting of copolyester and copolyamide; 20 to50 percent of silica; 2 to 10 percent of a long chain and/or cyclicfatty acid amide; and 0.5 to 5 percent of soap, said percents beingrelative to the weight of said master batch.
 5. The film of claim 1prepared by the flat film process.
 6. The film of claim 1 prepared bythe blown film process.
 7. The film of claim 5 wherein the processfurther comprises subjecting at least one surface of said film to atreatment selected from the group consisting of corona treatment, flametreatment and fluorine treatment.
 8. The film of claim 6 wherein theprocess further comprises subjecting at least one surface of said filmto a treatment selected from the group consisting of corona treatment,flame treatment and fluorine treatment.
 9. The film of claim 3 whereinsaid soap (b)(iii) has a chain length of 12 to 20 carbons.
 10. The filmof claim 9 wherein said soap (b)(iii) is a calcium salt.